Electrical control circuits



Match 1, 1932. H. L. PALMER ELECTRICAL CONTROL CIRCUITS Filed Jan. 29,1931 Inventor" Hart-g LPalmer His Attorney.

Patented Mar. 1, 1932 UNITED STATES PATENT OFFICE HARRY L. PALMER, FSCO'IIA, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COM.- PANY, A,CORPORATION OF NEW YORK ELECTRICAL CONTROL CIRCUITS Application filedJanuary 29, 1881. Serial No. 512,103,

My invention relates to electrical control circuits and particularly toautomatic control circuits for electric valves.

Control circuits of the bridge type for electric valves are well knownin the art. Such circuits usually comprise four impedances connected inthe form of a \Vheatstone bridge, at least two non-adjacent arms ofwhich have different thermal, voltage or current resistancecharacteristics. Stated more broadly the non-adjacent arms havecorresponding electrical properties whlch change relatively to eachother with similar changes in their electrical or physical condition.

Such an arrangement is, in effect, a reversing switch, with an offposition when all four arms have equal impedances, and reversing onpositions depending upon which air of non-ad'acent arms have the reaterimpedance. y connecting the ano e circuit of an electric valve to thesame source as supplies the input to the bridge, the operation of thebridge may be made to secure a reversal of polarity, or a 180 degreephase shift, in the grid potential of the valve with respect to itsanode potential.

In accordance with my invention I provide a novel and simplifiedcombination of a bridge control circuit and a hot cathode electriovalve, or valves, in that at least one valve filament is connected toform one of the arms of the bridge circuit. As these valves havefilaments, or heater elements, of tungsten, which has a comparativelyhigh positive temperature coefiicient. of resistance, they are readilyada tablefor use as the arms of bridge circuits. ucli use results in adistinct saving in that the cost of at least one of the usual bridgearms is eliminated while at the same time the steady power loss in thiselement is saved.

An object of my invention is to provide a novel static control circuitarrangement for an electric valve or valves.

My invention will be better understood from the following descriptiontaken in con nection with the accompanying drawing and its scope will bepointed out in the appended claims.

Referring now to the single figure of the positive temperaturecoefiicient of resistance.-

00 versing means by the reference character 2,

and the reversible motor by the character 3.

The control circuit is in a form of a \Vheatstone bridge having a pairof non-adjacent arms 4 and 5 composed of ordinary resistance material,such as iron, and a second pair of non-adjacent arms 6 and 7 com risingthe heater elements, or filaments, 8 an 9 of a pair of electricvalves.These heater elements are preferably connected to the bridge circuit bymeans of small filament transformers 10 and 11 as shown. The filaments,or heater elements, 8 and 9 are usually made of tun sten andconsequently they have a relatively iigh The input terminals ofthisbridge circuit are connected across one of the phases of a three phasepower supply circuit-12, while the output terminals of the bridge areconnected to the primary winding of a grid transformer 13.

When the voltageof circuit 12 is normal the arms of the bridge circuitare so adjusted that the two parallel paths between its input terminals,comprising respectively resistance 4 and filament 8 on the one hand andresistance 5 and filament 9 on the other hand, are equal in magnitude sothat no voltage appears across the primary winding of the gridtransformer 13. If now the voltage of circuit 12 should increase theincreased current flowing to the arms of the bridge will increase theresistance of the filaments 8 and 9 with the result that the bridge willbe unbalanced and an alternating voltage will appear across the primarywinding of transformer 13. Also, if the voltage of circuit 12 shouldfall the decrease in current in the bridge arms will decrease theresistance of the filaments 8 and 9 with the result that an alternatingvoltage of 100 opposite polarity, or a voltage shifted 180 de grees inphase will appear across the terminals of the primary winding oftransformer 13. It will thus be seen that when the voltage in circuit 12is normal no voltage is aplied to transformer 13 while increases and'ecreases of volta on circuit 12 cause alternating voltages 0 reversepolarity to be applied to this transformer.

The anode circuits of the valves are supplied with current from a supplytransformer 14, which is also connected across one of the phases of suply circuit 12. As shown, the electrical mi point of the secondarywinding of transformer 14 is connected to the filaments while theterminals of the secondary winding are connected res ctively to theanodes 15 and 16 of these va ves through actuating coils 17 and 18respectively of a air of reversing relays 19 and 20. I The secon arywinding of grid transformer 13 has one of its terminals connected to thegrids 21 and 22 of the electric valve through current limiting resistors23 and 24, while the other terminal of this secondary windin isconnected to the filaments through a grid bias battery 25.

Motor 3 is connected to be energized from supply circuit 12 through thereversing contactors, or relays, 19 and 20. As shown these contactorsare so connected that they reverse one of the phases of the power supplycircuit which is connected to this motor whenever one or the other ofthe relays is energized. This causes a reversal of motor 3 in a mannerwhich is well understood by those skilled in the art.

The electric valves may be either of the A high vacuum pureelectron-discharge type or the gas-filled type. I prefer, however, touse the gas-filled type because of their larger current-carryingcapacity.

The operation of the system illustrated in the drawing is as follows:Assume that sup ply circuit 12 is energized and that its voltage isnormal. Under these conditions the bridge circuit will be balanced, aspointed out above, no voltage will be applied to the grid transformer 13and both electric valves will be non-conducting because their grids areat the negative potential produced by the grid bias source 25.

If now the voltage of circuit 12 should decrease, an alternating volta ewill be produced by the secondary winc ing of trans-- former 13, asexplained above, and this voltage will be transmitted to the grids 21and 22 of the electric valves. This voltage will be in phase with theanode potential of one of the valves and will be 180 degrees out ofphase with the anode potential of the other valve because of the factthat the anode potentials of the two halves are themselves 180 degreesout of phase due to the way they are connected to the secondary windingof transformer 14. As a result the valve in which the grid potential isin phase with its anode potential will become conducting with the resultthat an anode current will flow through the operating coil of one of thecontactors 19 or 20. The result will be that motor 3 will be connectedto circuit 12 and the motor will then start to operate. If new, thevoltage of circuit 12 should rise above normal the potential of thesecondary winding of grid transformer 13 will reverse with the resultthat the other valve will become conducting, and the valve which hasbeen conducting will become non-conducting, thereby energizing theoperating coil of the other contactor and deencrgizing the operatingcoil of the first contactor with the result that the phase connectionsto motor 3 are reversed and the motor operates in a reverse direction.

Thus, for example, if the voltage of circuit 12 rises, the right-handvalve. may, for example, be made conducting with the result thatcontactor 19 operates and motor 3 runs in one direction, while if thevoltage in circuit 12 falls the left-hand electric valve be comesconducting and the .right-hand valve becomes non-conducting with theresult that contactor 20 will be energized thereby to reverse motor 3.

It should be understood that while I have shown my novel and simplifiedcontrol scheme as applied to a pair of valves which control contactorsfor reversin an electric motor, my invention is not so limited and thatthe scheme may be used in connection with any pair of valves which areto be selectively energized.

\Vhile I have shown and described a preferred embodiment of myinvention, it will be obvious to those skilled in the art that changesand modifications may be made with out departing from my invention and Itherefore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

.Vhat I claim as new and desire to secure by Letters Patent of thelnited States is,

1. In combination, an electric valve having a plurality of electrodesand means "for fchanging an electrical condition of one of saidelectrodes in accordance with changes in an electrical property of oneof said electrodes.

2. In combination, an electric valve having a plurality of electrodes.means responsive to an electrical condition of an electric circuit forcontrolling an electrical condition of one of said electrodes, saidmeans having at least two elements whose corresponding electricalproperties change relatively to each other, at least one of saidelements being an electrode of said valve.

3. In combination, a hot cathode electric valve and means forcontrolling the opera tion of said valve including a bridge circuit,

one of whose arms comprises the cathode of said valve.

4. In combination, a pair of hot filament electric valves and means forcontrolling I said valves including a voltage bridge, two of whose armsare composed of the filaments of said valves.

5. In combination, a voltage balance control device of the type havingtwo pairs of 10 impedances having diflerent temperature coefficients ofresistance, all connected in the form of a Wheat-stone bridge, a pair ofhot cathode electric valves connected to be controlled by said bridge,said cathodes formin one pair of impedance elements of sai bridge.

6. In combination, a device for producing a control voltage to beapplied to the control electrode of a three element electric 10 valvecom risin d a balance circuit including two impe ances aving dilferenttemperature coeflicients of resistance, a three element electric valve,and means connectin the filament of said valve as one of the impedancesof said 2! balance circuit.

7. In combination, a bridge circuit for controllin the operation of ahot cathode electric va ve, a hot cathode electric valve and a filamenttransformer connecting the cath- {0 ode of said valve into said bridgecircuit as one of the arms thereof.

8. In combination, a supply circuit, a load circuit, an electric valveincluding a cathode havin a variable coefiicient of resistance for I!contro lin the energization of said load circuit, a bridge circuitincluding the cathode of said valve and connected to be responsive to anelectrical condition of said supply circuit for controlling said valve.

40 9. In combination, an electric circuit, an

electric motor, circuit controlling means connecting said motor to saidcircuit so as to be operable in reverse directions, hot cathode e ectricvalves for controlling said circuit 48 controlling means, a. voltageresponsive bridge connected to control said valves in response tovariations in the voltage of said circuit, the cathodes of said valvesbeing connected to form two of the arms of said bridge. 60 In witnesswhereof I have hereunto set my hand.

HARRY L. PALMER.

